This invention relates to unique fabrics for use in web forming machines for making sanitary paper webs (e.g., tissue and towel stock) and other wet formed cellulosic sheets or nonwoven webs; most desirably patterned web products which are especially suitable for use in papermaking machines. Although the fabrics of this invention are particularly well suited for use as a forming wire in the forming section of a papermaking machine to make patterned sanitary paper products, it is within the scope of the broadest aspects of this invention to employ these fabrics for a variety of other applications in papermaking machine, e.g., as a transfer fabric or dryer fabric, particularly a through-air-dryer (TAD) fabric, as well as in nonwoven apparatus. For some applications one surface of the fabric is employed as the web-contacting, or engaging surface, whereas for other applications the opposed surface of the fabric may preferably be employed as the web-contacting, or engaging surface.
Reference throughout this application to a xe2x80x9cweb forming machinexe2x80x9d includes both papermaking and nonwoven machines.
Reference throughout this application to a xe2x80x9cweb forming fabricxe2x80x9d is not limited to use of the fabric in the forming section of a web forming machine, but includes uses in other areas of such web forming machines.
Web forming fabrics employed to make patterned fibrous webs are commercially available and a number of such fabrics are disclosed in existing patents, e.g., U.S. Pat. No. 6,237,644 (Hay et al.), U.S. Pat. No. 5,429,686 (Chiu), U.S. Pat. No. 6,203,663 (Chiu) and Swedish Patent No. 427,053 (Gusums Bruk AB). It is important that these fabrics be capable of use in forming fibrous webs having a desired balance of strength, caliper and absorbency (including absorbency capacity and rate).
The inventors herein are two of the four inventors of the inventions forming the subject matter of Hay et al. U.S. Pat. No. 6,237,644. This latter patent discloses tissue forming fabrics, particularly single layer structures, employed to form fibrous webs having a useful combination of strength, caliper and absorbency.
There is a continuing desire to provide fabric constructions capable of use to form fibrous webs having enhanced, or increased, strength, caliper, absorbent capacity and/or absorbency rate. In particular, there is a continuing need to achieve a desired balance among these various properties. Generally, just improving the strength of the formed web tends to result in a denser structure that often does not provide the desired absorbency rate and/or capacity required in tissue products.
There also is a benefit and desire for web forming fabrics having opposed surfaces, each of which can constitute a web-engaging surface, depending upon the specific application of the forming fabric in the web forming machine.
Thus, a continuing need exists for web forming fabrics capable of use in forming fibrous webs, e.g., tissue products, having a desired balance of strength, caliper, absorbency rate and capacity, and that also is versatile in use.
The above and other objects of this invention are achieved in a web forming fabric having a machine direction of intended movement on a web forming machine and a cross-machine direction substantially normal to said machine direction, wherein said fabric includes machine direction yarns disposed generally in the machine direction and transverse yarns disposed generally transversely to the machine direction, said fabric including on one surface thereof first and second substantially linear arrays of systematically distributed areas of high drainage, said first and second substantially linear arrays being oriented at an acute angle to the machine direction and at an acute angle to each other. The boundaries of each of said systematically distributed areas are defined by two pairs of adjacent sides, the adjacent sides of one pair being angled segments of one transversely extending yarn and the adjacent sides of the other pair being angled segments of a second transversely extending yam contiguous to said one transversely extending yarn.
In preferred embodiments of this invention the systematically distributed areas of high drainage in the web forming fabrics of this invention include within their boundaries only machine direction yarns.
In accordance with the preferred embodiments of a web forming fabric of this invention, each systematically distributed area in the first substantially linear array is separated from contiguous systematically distributed areas on opposite sides thereof and in the same substantially linear array by spaced-apart angled segments of a pair of single transverse yarns that are contiguous to each other.
In one preferred embodiment of this invention the systematically distributed areas in the first substantially linear array are separated from adjacent systematically distributed areas in the same first substantially linear array by an angled segment of a single transverse yarn, and the systematically distributed areas in the second substantially linear array are separated from adjacent systematically distributed areas in the same second substantially linear array by an angled segment of a single transverse yarn.
In another embodiment of this invention, the systematically distributed areas in the first substantially linear array are separated from adjacent systematically distributed areas in the same first substantially linear array by an angled segment of a single transverse yarn and the systematically distributed areas in the second substantially linear array are separated from adjacent systematically distributed areas in the same second substantially linear array by a plurality of contiguous angled segments of contiguous transverse yarns, said contiguous angled segments of contiguous transverse yarns providing areas of drainage lower than that of the systematically distributed areas.
In accordance with the preferred embodiments of this invention the machine direction yarns on the side of the fabric opposed to the side including the systematically distributed surface areas, each include relatively long floats over a plurality of adjacent weft yarns; preferably over at least six adjacent weft yarns. Most preferably, each of the continuous machine direction floats of each machine direction yarn floats over at least the same three contiguous weft yarns as an adjacent machine direction yarn, with the continuous machine direction floats of adjacent machine direction yarns partially overlapping each other in the machine direction.
In one embodiment, each relatively long machine direction float is over seven adjacent weft yarns, with each continuous machine direction float of each machine direction yarn being over at least the same four contiguous weft yarns as an adjacent machine direction yarn and with the continuous machine direction floats of adjacent machine direction yarns partially overlapping each other in the machine direction.
The side of the fabric opposed to the side including the systematically distributed surface areas is well suited for engaging, or contacting the web being dryed in a dryer section of a web forming machine; preferably in a through-air-dryer section of a papermaking machine. In particular, the long, partially overlapping machine direction floats of adjacent machine direction yarns establish excellent adherence of the web to a creping cylinder (e.g., a Yankee dryer) in the machine direction to provide for very effective creping of the web being formed.